Influence of Various Anaesthetics on the Cardiovascular Responses to Noradrenaline in Rats before and after Guanethidine

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Abstract
The influence of surgical anesthesia induced by ketamine, pentobarbital, pentobarbital-xylazine, or chloralose-urethane on blood pressure and heart rate was studied and the effects were compared with results in conscious and pithed rats. Blood pressure was significantly decreased by pentobarbital-xylazine. Heart rate increased in all groups except in pentobarbital-xylazine anesthetized rats. Generally, a fall in heart rate and blood pressure was observed during a 2 h anesthesia as compared to the initial values. The blood pressure response to noradrenaline was significantly lowered by ketamine, pentobarbital and chloralose-urethane anesthesia and the response of the heart rate, only by chloralose-urethane. Guanethidine 5 mg/kg i.v. significantly lowered the blood pressure in the ketamine, pentobarbital and chloralose-urethane anesthetized groups. The guanethidine induced potentiation of the hemodynamic effects of noradrenaline was considerably influenced by the anesthetic; the augmentation was greatest in pentobarbital and chloralose-urethane anesthetized rats. Chloralose-urethane is considered a suitable anesthetic in rats when studying the effects of noradrenaline and guanethidine. Following a single i.p. injection a surgical anesthesia of more than 2 h duration was obtained and the variance of the parameters studied was less than that following administration of the other anesthetics. Various effects of anesthetics unrelated to their anesthetic properties may obscure or even invalidate results obtained with drugs acting on the peripheral sympathetic nervous system.